Lung cancer is responsible for the most cancer-related deaths worldwide. This proposal aims at dissecting the signaling pathways perturbed in human lung cancer, with a focus on the mechanisms of DOK-mediated lung tumor suppression. DOK (downstream of tyrosine kinase) family proteins are signaling proteins that modulate tyrosine kinase signaling. We recently identified DOK-1, DOK-2, and DOK-3 as lung tumor suppressors, and we further hypothesize that they are negative regulators of oncogenic EGFR-RAS signaling. In our preliminary analysis, we find that Dok-1, Dok-2, and Dok-3 single, double, and triple knockout mice develop lung adenocarcinoma with a penetrance and latency dependent on the number of lost Dok alleles. Tumors from Dok null mice exhibit Akt and Erk activation, similar to models of EGFR- or KRAS-driven tumorigenesis. In human non-small cell lung cancer (NSCLC), we observe frequent genomic loss of DOK-2 with a concomitant reduction of DOK-2 mRNA expression. Strikingly, genomic loss of DOK-2 is strongly associated with EGFR mutation status. We therefore hypothesize that DOK-2 opposes lung tumorigenesis initiated by oncogenic EGFR and RAS. Moreover, we further hypothesize that variant alleles of DOK-2 (such as DOK-2L138S) could underlie lung cancer susceptibility. The purpose of this proposal is to determine the mechanisms of DOK-mediated lung tumor suppression vis--vis the EGFR-RAS pathway and to ascertain the relevance of variant DOK-2 alleles and non-pulmonary cellular compartments to the pathogenesis of DOK-null lung cancer with the following specific aims: (1) To define the role of DOK-2 in EGFR- and KRAS-mutant lung cancers. To this end, we will utilize already existing EGFR and KRAS bitransgenic and Dok-2-/- mouse models to determine if Dok-2 opposes mutant EGFR or KRAS-driven lung cancer in vivo. In a preliminary analysis, we find that Dok-2 does indeed oppose lung tumorigenesis initiated by KRASG12D. (2) To define the role of DOK-2L138S in lung cancer susceptibility. The DOK-2L138S allele is present both as a somatic mutation found in human lung cancer and as a naturally occurring germline polymorphism. In vitro analysis indicates that DOK-2L138S is a loss-of-function mutant that is defective at suppressing EGF-induced RAS and ERK activity. To determine if this allele contributes to lung cancer susceptibility, we will perform a case/control study of human lung cancer, and, in parallel, generate a Dok-2L138S knock-in mouse model. (3) Evaluate the contributions of cell autonomous and non-cell autonomous mechanisms to tumor formation in Dok mutant mice. The relevance of the Dok TKO hematopoietic phenotype will be determined using a reciprocal bone marrow transplant using wild-type and TKO animals. Furthermore, generation of a lung-specific conditional Dok-2 knockout mouse model will allow unequivocal determination of the contribution of cell autonomous mechanisms to the Dok-2 knockout lung phenotype. PUBLIC HEALTH RELEVANCE: Lung cancer remains responsible for the most cancer-related deaths every year, with a growing proportion of lung cancer found in never smokers. It is therefore imperative to deconstruct the molecular genetics and the pathways perturbed in human lung cancer. Our work will define the mechanism of tumor predisposition, initiation and progression in a DOK-null scenario, in both a somatic and inherited setting, and dissect the relationship of DOK-2 loss to EGFR and RAS. This work could identify additional targets for the prevention and treatment of human lung cancer and discover genetic criteria that determine tumor phenotype, progression, and response to therapy.